Graphic aid and methods related thereto

ABSTRACT

A master grid layout sheet and methods of manufacture associated therewith are disclosed for use in graphic art work such as the layout and reproduction of printed circuits and the like. In typical printed circuit work precision art work and subsequent photographic reproduction thereof are normal intermediate processing steps. The master sheet includes a pattern, usually of orthogonal reference lines, printed thereon in a predetermined critical gray or neutral monotone. The monotone has a visual density such that the reference line pattern is visible to a draftsman but the light transmission density or opacity thereof is insufficient to cause the pattern to be reproduced in a controlled photographic reproduction of the master sheet. A processing control method for forming the master grid sheet is also disclosed. The process utilizes a visual process control guide which provides a standard of comparison for obtaining the critical transmission density of the gray monotone pattern. Thus the development process by which the master grid sheet is formed may be consistently controlled to produce the critical transmission density for the reference pattern thereon. The subsequent processing of reproductions of the art work may be controlled in correlation with the critical density of the monotone pattern to cause the pattern to disappear in the final product.

United States Patent Baker [54] GRAPHIC AID AND METHODS RELATED THERETOElton N. Baker, Elgin, Ill. [73] Assignee: Fotel Inc., Villa Park, Ill.[22] Filed: May 13, 1970 [21] Appl. No.: 36,979

[72] Inventor:

[52] U.S. Cl ..95/85, 96/27 [51] Int. Cl. ..G03b 15/00 [58] Field ofSearch ..95/l, 85; 96/27 [56] References Cited UNITED STATES PATENTS3,169,063 2/1965 Johnston ..96/27 3,499,377 3/1970 Esses ..95/85 FOREIGNPATENTS OR APPLICATIONS 578,363 6/1933 Germany ..352/240 PrimaryE.raminer.lohn M. Horan AttorneyPendleton, Neuman, Williams & Anderson 5ABSTRACT A master grid layout sheet and methods of manufactureassociated therewith are disclosed for use in graphic art work (1513,657,983 51 Apr. 25, 1972 such as the layout and reproduction ofprinted circuits and the like. In typical printed circuit work precisionart work and subsequent photographic reproduction thereof are normalintermediate processing steps. The master sheet includes a pattern,usually of orthogonal reference lines, printed thereon in apredetermined critical gray or neutral monotone. The monotone has avisual density such that the reference line pattern is visible to adraftsman but the light transmission density or opacity thereof isinsufficient to cause the pattern to be reproduced in a controlledphotographic reproduction of the master sheet.

A processing control method for forming the master grid sheet is alsodisclosed. The process utilizes a visual process control guide whichprovides a standard of comparison for obtaining the criticaltransmission density of the gray monotone pattern. Thus the developmentprocess by which the master grid sheet is formed may be consistentlycontrolled to produce the critical transmission density for thereference pattern thereon. The subsequent processing of reproductions ofthe art work may be controlled in correlation with the critical densityof the monotone pattern to cause the pattern to disappear in the finalproduct.

11 Claims, 7 Drawing Figures PATENTED APR25 1972 SHEET 1 0F 2 FIG. 1

QPMS O 'UJ Tk. a 7.- W36 N n H I w l GRAPHIC AID AND METHODS RELATEDTHERETO FIELD OF THE INVENTION The invention is directed generally tomethods and apparatus for graphic reproduction and more particularly tothe preparation and photoreproduction of drafting in the production ofelectronic circuits.

I BACKGROUND OF THE INVENTION Many electronic devices such as printedcircuits and the like include one or more conductors which are, forexample, printed, plated, etched or formed by a chemical depositionprocess on a base of insulating material. Ordinarily one or more mastersheets including drawings or other pictorial representations of theconductors in accurate relative registration must first be made. Priorart methods and apparatus for drafting such electronic devices ofteninclude underlay reference grid sheets or color reference lines on themaster sheet itself. Similar layout grids are utilized in other areas ofthe graphic arts.

Underlay grid sheets introduce errors because of these shortcomings: (a)accidental grid shift is possible even though the reference is pinned ortaped to the master; (b) the master and reference grid must bemaintained in intimate contact during the layout process; (c)maintenance of circuit component placement cannot be checked once themaster is removed from the underlay grid; (d) the grid must be selectedto be ofthe same size as the master to prevent misregistration; and (e)it is difficult to interrupt a project once it is begun, or makerevisions, corrections or alterations thereon because of difficulties inre-establishing registration.

Producing color grid lines on master sheets, which are intended not toreproduce in subsequent photoreproduction, suffers from twomanufacturing shortcomings: (a) typical color images require, inaddition to regular exposure and processing, several very difficultoperations: a bleach-etch process, a manual re-development for blackimage detail, and a manual dye application for color lines; and (b)production control of the color intensity to provide both good draftingvisibility and subsequent total photographic drop out is difficult. Inaddition to manufacturing problems, the use of a color grid conflictswith the techniques of photographic color separation used to reproducefrom a master drafted with two color tapes.

SUMMARY OF THE INVENTION Thus it is an object of this invention toprovide a method and apparatus which avoids or minimizes all theaforenoted shortcomings.

It is another object ofthis invention to provide a master grid layoutsheet for use in graphic art work such as the layout of printed circuitsand the like where precise art work and photographic reproduction arerequisite intermediate steps, the master sheet including a pattern ofreference lines which are visible for circuit drafting purposes, butdrop out during the processing of a photographic reproduction of themaster sheet.

lt isa further object of this invention to provide a method forcontrolling the density of the reference lines during the I rocess ofproducing the master grid layout sheet, so that the qualities notedabove are consistently provided.

Further and additional objects will appear from the description,accompanying drawings and appended claims.

In accordance with one embodiment of this invention, a master layoutsheet is provided including a diaphanous base having both effectivelyopaque images which appear on both the master layout sheet and thereproduction thereof and a light gray or neutral monotone patterndisposed thereon. As

used herein the term effectively opaque means sufficiently dense toprovide sharply contrasting areas in the ultimate reproduction whichwill determine the printed circuit pattern,

and the term neutral monotone denotes a homogeneous neutral densitysubstantially less than effectively opaque."

The monotone pattern may comprise a network of orthogonal referencelines or the like and is of a precisely selected critical density, denseenough so that it is visible to an artist laying out a circuit design onthe master sheet, and yet sufficiently transmissive so that it will notbe reproduced in a properly processed photographic copy of the master.In order to precisely control the density of the monotone pattern, avisual processing control guide is incorporated in a selected area ofthe master layout sheet. The processing guide includes a test patchhaving the same density as the monotone pattern, and monotone orhomogeneous in nature, and a plurality of comparator patches which arenot monotone but, on the contrary are halftones or the like. Onecomparator patch is a standard patch having an average or effectivedensity bearing a known relationship to the density of the monotonepattern; The remaining comparator patches have effective densities whichestablish predetermined upper and lower limits for the density of themonotone pattern. Further, the comparator patches, because of theirnon-homogeneous character develop their final effective density morequickly than the monotone test patch thus establishing a standard ofcomparison which may be used to control the development of the monotonetest patch and thereby the pattern on the master layout sheet toprecisely the proper density. I v

IN THE DRAWINGS FIG. 1 is a plan view of a master layout sheet andvisual processing guide in accordance with this invention.

FIG. 2 is a detailed view ofa visual processing control guide for use intray processing ofa master layout sheet developed in accordance withthis invention.

FIG. 3 is a detailed view of an alternative processing guide for 'use inmachine processing of a master layout sheet developed in accordance withthis invention.

FIG. 4 is an illustration of a vacuum contact device for exposing asuitable sensitive film in producing a master layout sheet in accordancewith this invention.

FIG. 5 is a partially exploded side view of the vacuum contact deviceshown in FIG. 4 illustrating the relative placement of the elementsduring exposure of the sensitive film to produce the master layoutsheet.

FIG. 6 is a set of curves illustrating the relationship betweendevelopment time and visual effects in the visual processing guide ofFIG. 2 to achieve the optimum density of the gray monotone referencepattern on the 'master layout sheet.

FIG. 7 is a Hurter-Driffield characteristic curve of a sensitive filmsuitable for production of the master layout sheet of this invention. 1

Referring now to the drawings and in particular to FIG. I, a preferredembodiment ofa master grid layout sheet 2 is shown which is particularlysuited to close tolerance printed circuit art work. The grid layoutsheet is ofa diaphanous material and includes a pattern of orthogonalreference lines 10 on the surface thereof. The master can also includeboard corner marks 16, edge contact connectors 18 and other commonfeatures. In drafting a circuit on the master layout sheet, a draftsmanapplies a suitable adhesive tape to the master layout sheet 2,positioning the tape to represent theconductors of the printed circuit.The tape may be cut to desired lengths and applied to the master torepresent conductors 14, using the reference network lines 10 as guides.Through-board connections and terminal points may be applied in the formof printed or diecut self-adhesive pads 15 located using intersectionsof the reference lines 10 as guides.

The master layout sheet 2 is purposely of large dimensions, for example,four times the desired finished board size, so that after the desiredcircuitry configuration is achieved, the board may be reduced in size bya photographic reproduction process with enhanced precision in theultimate product. This reduction step causes any placement error in theprinted circuit configuration as laid out on sheet 2 to be diminished inthe same proportion as the master is reduced. The photographic reductionof the finished master sheet to final size is made on a camera such as agraphic arts darkroom type which reproduces the printed circuit art workwith minimal distortion of its geometry and to vary precise dimensions.In a typical manufacturing process the photographic reproduction, whichmay be positive or negative in form, may be used to produce a silkscreen mask for printing a resist on a suitable copper clad conductingboard, or to expose a light sensitive resist on a conducting board. Theresist selectively covers or exposes the copper circuits during platingor etching processes which remove the unwanted copper or add desiredprotective metallic layers in accordance with the pattern of tape on themaster sheet 2.

Thus the presence of the reference lines 10 on the master grid layoutsheet 2 during the art work layout process is very important in holdingdrafting errors to a minimum. However, should any of these referencelines appear on the photographic reproduction of the art work, anerroneous circuit connection of spurious metallic areas is produced inthe printed circuit board. If the reference lines 10 are to be visibleto a circuit draftsman working on the master layout sheet 2 but are notto appear on a photographic reproduction thereof, the transmissiondensity of the lines must be held within critical limits. Density, inphotographic work, is the logarithm (to the base 10) of opacity and isdefined by I (incident light) T (transmitted light) Therefore, DensityLog I/T. Thus if the incident light is designated as 100 percent, thefollowing examples will illustrate the meaning of density as applied tothis invention: (a) If all the light is transmitted (very nearly true ofglass), then the opacity would be unit and, since the logarithm of l is0, the density would be (b) If none'ofthe incident light weretransmitted (rarely encountered in photography), the opacity and densitywould be infinity; (c) If 50 percent of the light is transmitted, theopacity would be 2, and the log of 2, which is 0.30, would be thedensity; (d) If percent of the light is transmitted, the opacity wouldbe l0 and the density would be Opacity 1.0.0; and (e) If 0.] percentl/l0 of 1 percent) of the light is transmitted, the opacity would be1,000 and the density would be 3.00.

A table of Common Logarithms (to the base 10) will show theabove-defined relationship between opacity and density by readingopacity as the numberand density as the logarithm.

The Log l/T shall be referred to herein as transmission density. It hasbeen determined that the reference lines 10 on the master sheet 2 shouldhave a critical monotone density located within the general range of0.20 to 0.40 above base density of the film, and preferably have anoptimum critical transmission density of 0.30 controlled within 0.05density abovebase density. Clear film of the type described herein has abase density of 0.05 to 0.07 which is inherently compensated for in trayprocessing by the fact that both the processing guide and the referencepattern are referred to the same base density. In machineprocessing-where transmission density readings may be taken by adensitometer, the densitometer may be calibrated to read 0 (zero)through a clear area of this base film.

Monotone density (gray) as used herein applies to a single density valueof a typical photographic continuous or homogeneous tone. Effectivevisual density is used herein to designate the apparent density producedby the halftone technique which is used for the comparator patches ofthe processing guides. A halftone produces visual densities by thetechnique ofco ntrolling the ratio oftransmitted light to the in- Icident light, in accordance with the previous definition: Density LogUT. The halftone achieves this by the use of dots or lines having asingle high density value to effectively absorb a portion of theincident light. The ratio'of transmitted light is dependent upontheratio of the size of high density areas to clear areas. These dots orlines occur in regular, repetitive spacing of a frequency sufficientlyhigh to prevent visual processed as described herein. A monotonereference pattern having the prescribed critical transmission densityhas sufficient visual density to be visible to the naked eye and beusable in drafting the printed circuit art work as well as having atransmission density so low that the pattern will not appear in aphotographic reproduction of the completed printed circuit art work whenprocessed as describedherein. 'The'exact density value for the monotonereference pattern should preferably be maintained within a plus or minus0.05 limitaround the critical transmission density of 0.30 above basedensity in order to provide visibility of the reference pattern for thedraftsman without exceeding the upper density limit imposed by theexposure and processing parameters of the subsequent photographicreproduction.

High density (black) features which are common to a plurality of printedcircuit layouts, such as edge contact connectors 18, are printed on thesame master grid layout sheet.

' These features typically have a density not less than 3.00

above the density of the base. Some latitude in the density of the blackfeatures above this lower limit is permissible, with emphasis being onthe quality of image geometry and the sharpness so that these featuresare accurately portrayed in the photographic reproduction of the 'mastersheet. The parameters set forth herein are interrelated and depend inpart on the available materials. Variations are possible within thefunctional constraints set forth herein.

The use of accurately controlled methods of exposure and development inthe production of the master layout sheet insures that the monotonereference lines 10 will beeliminated in subsequent photoreproduction,whereas black features such as 18 will be sharply and clearly.reproduced. The method utilizes a processing guide 70 (shown in FIG. 1and explained in detail below) including a test area 78 of the optimummonotone density and a plurality of comparator patches 72, 74, 76specially designed to provide standards by which the development of thecritical low density levels may be monitored. These patches arepreferably non-homogeneous halftones.

The master grid layout sheet is exposed in a vacuum contact filmexposure device shown in perspective in FIG. 4. The exposure device 28includes a base 30 having an embossed blanket 32 incorporated therein.An outlet 34 to a vacuum pump (not shown) is mounted to the underside ofthe base 30 and communicates with the embossing of blanket 32.Registration pins 35 and 36 and film cover sheet 38 are affixed to theupper side of the base. The base may be made of rigid acrylic plasticand the embossed blanket of black flexible vinyl plastic to providemeans for air evacuation, thereby providing vacuum contact between theelements of the exposure device during the exposure process describedbelow, while maintaining a nonreflective background for the exposure ofthe film therein. The cover sheet 38, which may be 0.004 inch Mylar, isused to sandwich a sensitive film 40 to be exposed and an image bearingnegative 42 through which the exposure is made in intimate contactbetween cover 38 and blanket 32. A channel 39 provides communicationbetween the vacuum outlet 34 and the blanket 32 to draw the cover sheet38 down tightly on the sensitive film and master negative.

The procedure for exposing a sensitive film 40 to print thereon both theoptimum density monotone pattern of reference lines and the high densitystandardized circuit features (which are to carry over into the finalprinted circuit) will now be explained in detail with reference to thepartially exploded view of the'exposure device in FIG. 5. Thearrangement for making an exposure places the sensitive film 40(emulsion up) over blanket 32 covered in turn by master negative 42(emulsion down) and cover sheet 38.

As shown in characteristic response curve FIG. 7, the emulsion anddeveloper are carefully chosen to provide a curve portion of low gammaor contrast embracing the low density (gray) levels as well as a curveportion of high gamma so the development of a low density may becritically controlled without sacrificing the high density capabilityrequired for the black images. Kodaline Ortho Estar Base 0.007 developedin DuPont 24D meets these requirements and is the combination used forthe evaluation in FIG. 7. There are other satisfactory combinations ofemulsions and developers including some films which have a matte surfaceor are effectively translucent.

During exposure ofsensitive film 40, the master negative 42 is held inalignment overlying the film by register pins 35 and 36. The sensitivefilm 40 and master negative 42 are sandwiched in overlying registrationby cover 38 and the vacuum pump is started. A soft pile roller such as apaint roller sleeve may be used to assist in the evacuation of air frombetween film 40 and negative 42 to promote intimate contacttherebetween. A first exposure of the entire image of the masternegative is made from the low intensity light source 60, FIG. 4, byusing a timer (not shown) to control the exposure duration.

Prior to the second exposure, without releasing the vacuum, an area mask62 is placed in register, using register pins 35 and 36, over thecorresponding areas of the master negative and squeegeed fiat to thecover sheet. Vacuum contact for the mask is not required because itcontains no fine details. This mask blocks out the areas to be developedto the gray monotone density but is open in the areas for the blackimage details such as the edge contact connectors 18 and the comparatorpatches of the processing guide 70. The second exposure is made from thehigh intensity light 64. Both exposures are made for the same timeincrement, typically about seconds, controlled by a reset timer. The twolight sources 60 and 64 have a light intensity ratio of about 1 to 10which represents 21 Log Exposure difference of L00. A switch directs thetimer output to the appropriate light source. The power supply of thetimer is provided by a voltage regulating transformer to insure aconsistent intensity ofthe light sources.

.An optional third exposure step may be added to the method detailedabove to add patch areas of the gray monotone density outside the areaof the monotone reference linesv For example, some fine details such asregister marks and dimension lines which are drafted onto the mastergrid layout sheet require more critical exposure at the final reductionthan employed for bolder high density (black) features and the draftedcircuit details. The fine details can be protected from overexposure andblooming" from adjacent clear areas by including a gray patchoverprinting the fine lines, the patch to be ofthe same monotone densityas used for the pattern of monotone reference lines. Prior to thisadditional exposure, the vacuum is released and overlay mask 62 andmaster negative 42 are removed. A mask (not illustrated) having openareas for these patches but with complete opacity to protect all otherareas is located in register in place of the master negative. The vacuumis again applied and another exposure is made from the low intensitylight source 60. The vacuum is released and the film is now ready forthe controlled processing procedure.

It should be understood that modifications of the exposure process maybe made without departing from the invention, provided only that theinterrelationship of parameters is maintained. For example, a singlelamp may be used for the exposures with proper adjustment ofthe exposuretimes. In another method, a single exposure is made with a single lightsource. This method is carried out by incorporating a mask of uniformdensity over all areas of the master negative which are to appear in lowdensity monotone. The density of the mask should be approximately 1.00,which will provide the necessary I to 10 exposure ratio between the lowdensity and high density patterns of the master. A single exposure isthen made using high intensity light 64. The aforementioned methods alluse a single master negative. Another method uses two or more masternegatives, each contributing a portion of the total image with eachreceiving its appropriate exposure.

In developing the exposed sensitive film 40, the density of the graymonotone portions within the optimum limits is a critical productionrequirement. At the same time the black features must be reproduced atthe maximum transmission density to provide effective opacity. Obviouslythe vuse of instrumentation such as a densitometer is not possibleduring tray development and therefore the use of the visual controlguide, FIG. 2, is imperative for manual processing. A densitometer maybe used to monitor samples with machine processing; however, the visualmachine processing guide, FIG. 3, appearing on each master provides aninstant and convenient evaluation. Therefore, either of the processingcontrol guides 70 in FIGS. 2 and 3 may be used in the developmentprocessing step to enable the operator to consistently produce mastersheets having monotone line patterns within the optimum gray densityrange.

The tray processing control guide, shown in FIG. 2, preferably includesat least three comparator density patches, indicated generally at 72, 74and 76 which quickly attain and thereafter maintain a stable visualdensity over a wide range of development changes during processing offilm 40, and a monotone sample patch 78 which develops to transmissiondensity at the same rate as the monotone reference pattern during thedevelopment process.

The changes in visual density with development time of the comparatorpatches 72-76 and the test patch 78 are illustrated in the graph of FIG.6. As shown therein, the developing process is terminated when apredetermined ocular relationship between the density of the comparatorpatch 74 and the test patch 78 is achieved. In the preferred embodimentthe comparator patches comprise halftone patterns of saturated highdensity areas interspersed with clear or low density areas to producevisual tones of a desired effective visual or optical density. The threeexemplary patches are comprised of three different halftones varying inthe ratio of opaque to clear area, the central patch being a halftonehaving an effective visual density bearing a known relationship to thegray monotone density to be used for the master sheet reference lines.The left-hand patch 72 is a submarginal halftone having an effectivevisual density too light to be consistently visible for use as areference line, and the right-hand patch 76 has an effective visualdensity so dark that a monotone reference line of this density mightcarry over into a photographic reproduction of the master layout sheet.The monotone test patch 78 is matched to the halftone patch 74 of thereference pattern. As shown in the graph of FIG. 6, the comparatorpatches which are exposed to halftone patterns develop rapidly and thenmaintain a nearly constant visual density, thereby establishing theoptimum density of the monotone reference pattern. These can be observedby reflection during the developing step under an appropriate safelight.

Processing of the sensitive film exposed by the method disclosed aboveto produce a master grid layout sheet having reference lines of optimumdensity as disclosed above can be done manually with trays or by anautomatic processor. The design for a control guide for manualprocessing is shown in FIG. 2. The curves of FIG. 6 illustrate therelationship between development time and certain visual densitycharacteristics of the comparator and test patches which are used tocontrol processing. The guide is designed to give an operatorcontrolling the developing operation a visual standard ofcomparisonbetween three comparator densities or tones and the density or tone ofthe gray monotone. The ideal effective visual density value ofcomparator patch 74 is designated by zero (0) with upper and lowerlimits designated minus and plus in patches 72 and 76 to aid theoperator in making an evaluation. The operator stops the developing stepwhen the density of the monotone test patch 78 appears to have a density between the plus and minus extremes of the reference patch tones 72and 76 with the objective of achieving a visual match 88, FIG. 6,between the monotone test patch 78 and comparator patch 74, at whichtime the film is transferred to a stop bath and then a fixing bath.

The visual densities of the halftone comparator patches are stable overa wide time period of the development cycle, as indicated byrespectively labelled curves 80, 82 and 84. The visual density or toneof gray monotone sample patch 78 slowly increases during development;the development process is stopped when a visual tone match is achievedbetween the tone of sample patch 78 and comparator patch 74. Observationof this guide is made under low visibility conditions, namely:reflectance from the emulsion while in the developer solution under safelight illumination. Thus the visual relationship between the monotonepatch 78 and the comparator patches 72, 74 and 76 is not the same astheir measured transmission densities, as illustrated in FIG, 6. It hasbeen determined that the observed patch 78 appears denser duringdevelopment by approximately 0.20 than its actual density, This apparentincrease in visual density of the monotone patch over the actualmeasured value of the critical transmission density is consistentthroughout the development process and thus requires no other correctionin the comparator and test patches of the visual processing guide thanan initial adjustment of the black to white ratio in the originalhalftones to increase the apparent density by about 0.2. Thus thehalftone comparator patch 74 should have a measured transmission densityof 0.50, which is two-thirds opaque to onethird clear, to matcheffectively a monotone density of 0.30. The ratio of opaque to clearportions in halftone patches 72 and 76 should be about 1.5:1 and 3:1respectively. With reference to the halftone patterns of the comparatorpatches ofthe processing guide, it should be noted that a line frequencyof about 50 lines per inch is about the minimum which the operator seesas an effective visual tone without resolving the lines under manualprocessing conditions.

FIG. 3 illustrates typical comparator patches incorporated in a visualprocessing guide for machine processing of the film carrying the mastergrid layout sheet. The guide differs from that of FIG. 2 because it isused as a standard of comparison after completion of processing, andprovides the operator with an evaluation useful in machine adjustments(speed and temperature) and chemistry changes (developer aging,additions or replacement) to control the development of filmsubsequently fed into the processor. More than three comparator patchdensity values are used because the magnitude of deviation should beevaluated to aid an operator in making the adjustments noted above. InFIG. 3, seven patches 90-96 are used with the center patch 93 providinga visual density match with the critical gray monotone density. A tableof ratios of opaque to clear portions of these halftone patches is setout below. It should be understood that these values are disclosed asexamples, and are not intended to be limiting in any way.

Patch 90 0. Patch 91 0. Patch 92 0.7 Patch 93 Patch 94 1. Patch 95 l.Patch 96 1.8

- It should also be noted that the automatic film processing guide isviewed under better conditions than the guide used in tray processingmethods, Therefore, the line frequency of the automatic processing guideof FIG. 3 should be higher to prevent visual resolution. A linefrequency of about 65 per inch is about minimal. Further, the apparentvisual density of the test patch 78 as observed is more nearly identicalto its actual transmission density so that no adjustment (as for themanual processing guide of FIG. 2) need be made. In fact, a densitometermay actually be used.

While a particular embodiment of this invention is shown above anddescribed, and articular methods of utilization are course, that theinvention is not to be limited thereto, since many modifications may bemade. It is contemplated, therefore, by the appended claims, to coverany such modifications as fall within the true spirit and scope of thisinvention.

I claim:

1. A layout sheet having disposed thereon a master reference pattern foruse in the preparation of photographic reproductions of effectivelyopaque effects on said sheet and oriented with respect to said masterreference pattern, the effects including a plurality oforientedeffectively opaque areas, said sheet comprising a generally planarmember having low optical density and a master reference pattern thereoncomprising neutral monotone effects disposed on a surface of said planarmember, the neutral monotone effects being disposed on said surface in apattern to facilitate the location of said of fectively opaque areas,said neutral monotone effects having an optical density sufficient to bevisible during the location of said effectively opaque areas but havingsufficiently low optical density that sufficient light impinging thereoncan be utilized in subsequent photographic reproduction to render saidneutral monotone effects photographically invisible, the optical densityof said neutral monotone effects being no more than about 0.4 above theoptical density of said planar member.

2. The layout sheet of claim 1 wherein said planar member is adiaphanous flexible sheet.

3. The layout sheet of claim 1 wherein said monotone effects and saidopaque areas are of the same color.

4. The layout sheet of claim 3 wherein the neutral monotone effects havelight transmission densities within the range of about 0.2 to about 0.4abovethe light transmission density of said planar member.

5. The layout sheet of claim 4 including opaque areas havingsubstantially the same color as neutral monotone effects and havinglight transmission densities of at least about 3.0 above the lighttransmission density of said planar member.

6. The layout sheet of claim 3 wherein the light transmission density ofsaid planar member is substantially zero.

7. The layout sheet of claim 6 wherein the density of said neutralmonotone effects is about 0.3.

8. A layout sheet having disposed thereon a master reference pattern foruse in the preparation of photographic reproductions of effectivelyopaque effects on said sheet and oriented with respect to said masterreference pattern, the effects including a plurality of orientedeffectively opaque areas, said sheet comprising a generally planarmember having low optical density and a master reference pattern thereoncomprising neutral monotone effects disposed on a surface of said planarmember, the neutral monotone effects being disposed on said surface in apattern to facilitate the location ofsaid effectively opaque areas, saidneutral monotone effects having an optical density sufficient to bevisible during the location of said effectively opaque areas but havingsufficiently low optical density that sufficient light impinging thereoncan be utilized in subsequent photographic reproduction to render saidneutral monotone effects photographically invisible, said generallyplanar member comprising a sheet of supporting film for a photographicemulsion, said neutral monotone effects constituting a pattern ofphotographic emulsion disposed on said film and reduced to a visiblestate.

9. The layout sheet of claim 8 wherein the neutral monotone effects havelight transmission densities within the range of about 0.2 to about 0.4above the light transmission density of said planar member. 7

10. The layout sheet of claim 8 wherein at least some of saideffectively opaque areas are areas of said photographic emulsion reducedto a visible state.

11. The layout sheet ofclaim 8 wherein at least some of said effectivelyopaque areas are adhesively secured to said film.

1. A layout sheet having disposed thereon a master reference pattern foruse in the preparation of photographic reproductions of effectivelyopaque effects on said sheet and oriented with respect to said masterreference pattern, the effects including a plurality of orientedeffectively opaque areas, said sheet comprising a generally planarmember having low optical density and a master reference pattern thereoncomprising neutral monotone effects disposed on a surface of said planarmember, the neUtral monotone effects being disposed on said surface in apattern to facilitate the location of said effectively opaque areas,said neutral monotone effects having an optical density sufficient to bevisible during the location of said effectively opaque areas but havingsufficiently low optical density that sufficient light impinging thereoncan be utilized in subsequent photographic reproduction to render saidneutral monotone effects photographically invisible, the optical densityof said neutral monotone effects being no more than about 0.4 above theoptical density of said planar member.
 2. The layout sheet of claim 1wherein said planar member is a diaphanous flexible sheet.
 3. The layoutsheet of claim 1 wherein said monotone effects and said opaque areas areof the same color.
 4. The layout sheet of claim 3 wherein the neutralmonotone effects have light transmission densities within the range ofabout 0.2 to about 0.4 above the light transmission density of saidplanar member.
 5. The layout sheet of claim 4 including opaque areashaving substantially the same color as neutral monotone effects andhaving light transmission densities of at least about 3.0 above thelight transmission density of said planar member.
 6. The layout sheet ofclaim 3 wherein the light transmission density of said planar member issubstantially zero.
 7. The layout sheet of claim 6 wherein the densityof said neutral monotone effects is about 0.3.
 8. A layout sheet havingdisposed thereon a master reference pattern for use in the preparationof photographic reproductions of effectively opaque effects on saidsheet and oriented with respect to said master reference pattern, theeffects including a plurality of oriented effectively opaque areas, saidsheet comprising a generally planar member having low optical densityand a master reference pattern thereon comprising neutral monotoneeffects disposed on a surface of said planar member, the neutralmonotone effects being disposed on said surface in a pattern tofacilitate the location of said effectively opaque areas, said neutralmonotone effects having an optical density sufficient to be visibleduring the location of said effectively opaque areas but havingsufficiently low optical density that sufficient light impinging thereoncan be utilized in subsequent photographic reproduction to render saidneutral monotone effects photographically invisible, said generallyplanar member comprising a sheet of supporting film for a photographicemulsion, said neutral monotone effects constituting a pattern ofphotographic emulsion disposed on said film and reduced to a visiblestate.
 9. The layout sheet of claim 8 wherein the neutral monotoneeffects have light transmission densities within the range of about 0.2to about 0.4 above the light transmission density of said planar member.10. The layout sheet of claim 8 wherein at least some of saideffectively opaque areas are areas of said photographic emulsion reducedto a visible state.
 11. The layout sheet of claim 8 wherein at leastsome of said effectively opaque areas are adhesively secured to saidfilm.